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From joshelser <...@git.apache.org>
Subject [GitHub] accumulo pull request #220: ACCUMULO-4591 replication latency metrics added
Date Thu, 23 Feb 2017 18:12:48 GMT
Github user joshelser commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/220#discussion_r102778301
  
    --- Diff: server/master/src/main/java/org/apache/accumulo/master/metrics/Metrics2ReplicationMetrics.java
---
    @@ -58,6 +59,7 @@ protected void snapshot() {
         registry.add(PENDING_FILES, getNumFilesPendingReplication());
         registry.add(NUM_PEERS, getNumConfiguredPeers());
         registry.add(MAX_REPLICATION_THREADS, getMaxReplicationThreads());
    +    registry.add(LATENCY, getLatencyInSeconds());
    --- End diff --
    
    You're collecting the "maximum" latency in the system which isn't ideal as it paints a
very skewed picture of the actual system.
    
    For example, if you have a single file which cannot be replicated (say, it's corrupted)
it would have a very long latency. The rest of the files may be replicating in a (hypothetically)
5seconds. The maximum latency would continue to increase without bound, indicating to an operator
that the system is not healthy, when the system is actually 99% healthy.
    
    Hadoop metrics2 exposes a histogram class for metrics which automatically aggregates min,
median, avg, max as well as percentiles (e.g. p75, p85, p95, p98, p99).


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